Both human basophils and mast cells arise from CD34+ progenitor cells. Messenger RNA's for the alpha, beta, and gamma subunits of the high affinity IgE receptor are coordinately expressed during the first few days of culture of murine bone marrow coincident with the appearance of mononuclear cells bearing high affinity IgE receptors. IgE receptor positive cells purified by FACS have been demonstrated to develop into mature mast cells. Mast cells adhere to surfaces coated with laminin. This process is enhanced by IgE-mediated activation but may occur in the absence of histamine release. Mast cell attachment to laminin depends upon a five amino acid (IKVAV) sequence. When mast cells attach to laminin, they decrease c-myc, but increase c-fos expression; and the levels of nuclear factors for c-AMP responsive elements increase. Murine mast cells also adhere to fibronectin, a process which is also dependent upon mast cell activation. Adhesion is inhibited by the RGDS peptide. A 120 kD fragment of fibronectin containing an attachment region mimics the activity of the native molecule. IL-3 dependent murine mast cell lines have been established by infecting bone marrow mast cells using AD12-SV50 hybrid virus. Cell lines established are similar to mast cells grown in primary culture from bone marrow. Mast cells synthesize heparan sulfate, collagen IV, and laminin which are the principle components of basement membrane. FCERI crosslinking in primary mast cell cultures results in the induction of multiple cytokine genes; significant levels of RNA for TGF-beta can be found in resting mast cells; cytokine genes can be divided into two groups (pro-inflammatory and growth factors) based on the intensity of the RNA signal and the time course of expression; and the expression of these groups appears to be regulated by distinct mechanisms. Dexamethasone added to cultured mast cells inhibits RNA synthesis.